Robot 'Mermaids' Swim Seas to Detect Seismic Waves

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Robots called "Mermaids" now floating in the oceans are helping
to create images of the Earth's interior.

Each robot is known as a Mobile Earthquake Recorder in Marine
Areas by Independent Divers, or Mermaid. They are equipped with
hydrophones, or underwater microphones, with which they record seismic waves from quakes and other
earth-shaking phenomena as they ripple through the water. The
mics can pick up the waves of quakes from as far away as 7,450
miles (12,000 km).

"Seismologists use seismic waves very much as X-rays," said
researcher Yann Hello, a geophysicist at the University of Nice
Sophia Antipolis in Villefranche-sur-Mer, France.

For instance, seismic waves slow down when they hit hotter rock
and speed up when they encounter colder rock, and "we
analyze this information and translate it into a picture of the
hot and cold regions inside the Earth," Hello told
OurAmazingPlanet.

The heat-driven motions of rock in the deep Earth underlie the
movements of continents and the earthquakes that can devastate cities, so
having a more detailed picture of what's happening beneath our
feet could better prepare us for such natural disasters.

One problem facing the effort to "see" what's happening down
below is the vastness of the Earth's oceans. There are very few
seismic stations in the oceans, which cover nearly three-quarters
of the Earth, leading to gaps in our picture of the world's
interior. Having robots out there can thus help fill in our
picture of the deep Earth, Hello said.

The Mermaids float freely about 3,300 to 6,500 feet (1 to 2
kilometers) below the ocean's surface. During the initial testing
of the robots, currently under way, they surface after recording
data for a short time so that researchers can gather their data.

In the future, the robots will surface only after detecting powerful seismic waves,
transmitting their data to satellites before returning to
their floating depth. Each robot carries a GPS unit to provide
its location, as well as sensors for temperature, salinity and
ocean current strength.

Two prototype Mermaids have just completed their longest
autonomous trips so far. One had a carbon hull, the other,
aluminum. The carbon hull is lighter, helping a robot carry more
batteries and work for longer in the field, but the aluminum hull
proved less sensitive to perturbations in the water and
ballasting errors.

Achieving new depths

Launched in June in the Ligurian Sea just south of Nice, France,
these prototypes were programmed to dive to a series of cruising
depths, surfacing after each new depth was maintained for three
or four days. They detected a strong earthquake 5,870 miles
(9,450 km) away, a magnitude 7.4 temblor near the Fox Islands off
the coast of Alaska. [Related: Seafloor Sensors Listen to Quake
Rumblings ]

The first fleet of a half-dozen fully operational aluminum-hulled
Mermaids will be launched in the Indian Ocean in the second half
of 2012. Their hardware will allow for oceanographic, weather,
biological and seismological observations, researchers said.

The technology of these robots will only improve over time,
researchers added. Scientists and engineers are now refining the
artificial intelligence algorithms that help the Mermaids decide
what seismic waves are meaningful or not, and are hoping to
develop larger and more lightweight floats with batteries that
allow them to survive for up to five years.

The scientists detailed their findings in the Oct. 4 issue of the
journal Eos.